The present invention relates to a scheduled motion planning method and apparatus for a vehicle and more particularly to a scheduled motion planning method and apparatus suited to a rendezvous and docking of a space vehicle.
Phase plane control (hereinafter called Prior Art 1) is one of the orbit control methods for space vehicles which are used conventionally by operators of space vehicles or control system designers.
FIG. 5 shows characteristics of phase plane control which are displayed on a phase plane. This control is independent in the three axes of x, y, and z. In FIG. 5, the horizontal axis represents a position deviation 401 between the desired position and position data and the vertical axis represents a velocity deviation 402 between the desired velocity and velocity data. In a + (plus) region 403 shown in the drawing, a control command is issued to a space vehicle so as to accelerate in the + (plus) direction. In a - (minus) region 404, the control command is issued to a space vehicle so as to accelerate in the (minus) direction. In a 0 (zero) region 405 (dead band), the control command is 0. The 0 region 405 is generally designed to be sufficiently wide compared with measurement errors of the position data and velocity data.
FIGS. 6 and 7 show response examples under the phase plane control.
In FIG. 6, the horizontal axis represents time and the vertical axis represents velocity. In the drawing, a desired velocity 411, an actual velocity 412, and a velocity 413 inputted to the controller (data measured by the sensor which is filtered) are shown. Although the actual velocity 412 overshoots the desired velocity 411, it is robustly stable for the measurement error.
FIG. 7 shows a locus 414 on the phase plane at this time (locus of the relationship between the position deviation and velocity deviation which are inputted to the controller).
As one of the means for suppressing overshooting, a method for presetting a temporary desired value and switching the desired value in appropriate timing (hereinafter called Prior Art 2) is proposed in Japanese Patent Application Laid-Open No. Heisei 5-127701.
The temporary desired value is designed so that the peak value when the actual velocity overshoots the desired velocity becomes equal to the original desired value and when the actually controlled value reaches the original desired value, the desired value is switched. This method does not preset the switching timing.
As one of other control methods, a method using predictive fuzzy control (hereinafter called Prior Art 3) is proposed in Journal of Japan Society for Aeronautical and Space Sciences, Vol. 39, No. 444, p 44 to 50, 1991.
In this method, a control command is decided by fuzzy inference of an evaluation function for three types of velocities when the velocity of a space vehicle is changed from the present velocity by .+-. delta and when it is left unchanged. In this case, by using an example of orbit control in the final approach phase of rendezvous and docking of the space vehicle, the magnitude of relative distance, upper and lower velocity limits, arrival time, and avoidance of collision (safety) are selected as evaluation items.
Rendezvous and docking of a space vehicle is generally divided into several phases depending on the flying method. For example, there are phases of orbit input, transfer, fly- around, final approach, and docking available. It is desirable in this case to make a scheduled motion plan from start to end for at least one phase and to let an operator know the scheduled motion plan. By doing this, the operator can predict the safety to a certain extent.
It is necessary that the scheduled motion plan itself can be changed depending on the status. By doing this, a disturbance, failure, or abnormal phenomenon can be properly dealt with.
Furthermore, an attempt to control the evaluation items precisely one by one like Prior Art 3 is also a method. However, it may be considered to use the control system like Prior Art 1 which is conventionally used by users and control system designers and to make a scheduled motion plan so as to put the characteristics of the control system to practical use. For example, under the aforementioned phase plane control, it is known that overshooting can be improved by setting the desired velocity in stages like Prior Art 2.